The　popular　Structural　SIMilarity　(SSIM)　index　has　shown　to　be　a　good　perceptual　criterion　for　testing　and　optimizing　video　encoders　such　as　the　MPEG-H/H.265　High　Efficiency　Video　Coding　(HEVC).　However,　it　is　still　unclear　how　to　compare　two　HEVC　encoders　with　a　number　of　bit　rates　and　SSIM　values.　In　this　work,　we　study　the　video　quality　comparison　of　HEVC　encoders　based　on　the　Bit　Rate-SSIM　(R-S)　curves.　Our　contributions　are　three-fold.　First,　we　exploit　how　to　interpolate　an　R-S　curve　when　only　a　small　number　of　R-S　samples　are　available.　We　also　develop　to　minimize　the　weighted　sum　of　squared　errors　during　the　interpolation　process,　where　the　weights　are　pre-defined　by　users　to　satisfy　the　diversified　requirements.　Second,　we　propose　an　approach　to　evaluate　the　perceptual　coding　gain　in　terms　of　the　R-S　improvement　between　two　individual　video　encoders.　Third,　as　an　application,　we　utilize　the　proposed　approach　to　compare　the　R-S　performances　of　HEVC　encoders　with　different　configurations.　©　2015　Asia-Pacific　Signal　and　Information　Processing　Association.